Due to the different layout of the aircraft, there are various ways of landing gear. The nose gear is housed in the front fuselage, while the main landing gear can be housed in the wing, in the wing and fuselage, in the fuselage, in the engine nacelle or in a special landing gear nacelle.

The force form and motion map of the retractable landing gear have a series of features:

a. The force form of the landing gear is beam type;

b. Under the load in the retracting plane, the force form of the landing gear belongs to the static force system in structural mechanics;

c. According to the mechanical principle, the movement diagram of the landing gear during the retracting process forms a four-bar linkage mechanism or a four-link hinge mechanism to ensure the geometric invariance and retracting movement of the force-receiving system;

d. The actuator should be left with an appropriate alternate stroke;

e. In the retracting movement, it is necessary to avoid excessive changes in the force on the actuator, and the efficiency of the retracting movement should be ≥50%;

f. The pillars must have supportive support to withstand the forces from the vertical retraction plane;

g. There must be sufficient clearance between the parts of the retractable structure.